The Applicant has developed a range of Memjet® inkjet printers as described in, for example, WO2011/143700, WO2011/143699 and WO2009/089567, the contents of which are herein incorporated by reference. Memjet® printers employ a stationary pagewidth printhead offering the advantages of high-speed printing and noise reduction compared to conventional scanning inkjet printers.
In a typical media feed mechanism, a media sheet (e.g. paper) is picked from a media tray using a media picker, which typically comprises a rubberized roller. The sheet is fed around a C-chute and into the nip of a main drive roller assembly positioned upstream of the printhead. The drive roller assembly comprises a drive roller engaged with an idler roller, with the drive roller controlling the speed of the media as it travels through the print zone opposite the printhead. From the print zone, the media sheet is delivered to an output tray generally positioned above the media tray. One or more intermediary drive roller assemblies may be positioned between the picker and the main drive roller. The intermediary drive assists in guiding the media sheet around the C-chute and into the nip of the main drive roller assembly.
Media skew is potentially problematic in printers, especially high-speed printers. Potential sources of skew include, for example, picker alignment, media tray alignment to the printer, media alignment within the media tray, different drag forces on opposite side edges of the media, media stiffness variations etc. Any media skew as the media travel around the C-chute is transmitted into the print zone resulting in skewed printouts. Minor skew variations are barely noticeable to most users; however, skew variations become more noticeable in bound multi-page documents. Moreover, duplexed printing requires the same media sheet to pass through the print zone twice, so that any media skew on the first pass tends to be exacerbated on the second pass.
Media feed mechanisms also require accurate coordination between the various roller assemblies. Typically, a system of sensors is employed to monitor the position of the media sheet around the media path, and a controller uses feedback from the sensors to coordinate operation of the various rollers.
It would be desirable to simplify coordination of an intermediary drive roller assembly and a main drive roller assembly in a media feed mechanism for a printer. It would further be desirable to provide a media feed mechanism, which minimizes skew in media sheets as they pass through the print zone of a printer.